1. Field of the Invention
The present invention relates to a vehicular electric power generating system having a vehicular electric generator rotatable by an engine mounted on a vehicle.
2. Description of the Related Art
Conventional vehicular electric generators are rotated at a certain speed increasing ratio by the vehicle-mounted engine while the vehicle powered thereby is traveling. Recent vehicle-mounted engines have a tendency to idle at lower idling speeds to meet demands for reduced exhaust emission and reduced fuel consumption. Since such lower idling speeds result in a reduction in the operating speed of vehicular electric generators, the ability of the vehicular electric generators to supply electric power to various electric loads on vehicles is also lowered. Nevertheless, modern vehicles demand more electric power as various devices and units mounted on the vehicles are more and more computerized. Accordingly, greater difficulty is being experienced in keeping the operating point of vehicular electric generators in an optimum range. One solution is to rotate a vehicular electric generator in combination with a device for transmitting the rotation of an engine at a variable speed ratio to the vehicular electric generator. For details, reference should be made to Japanese laid-open patent publication No. 2001-103796 (pages 3 and 4, FIGS. 1 through 10), Japanese laid-open patent publication No. H09-9413 (pages 3 through 6, FIGS. 1 through 4), Japanese laid-open patent publication No. H11-125318 (pages 3 through 7, FIGS. 1 through 6), and Japanese laid-open patent publication No. 2003-264995 (pages 2 through 4, FIGS. 1 through 4). The power generating efficiency of the vehicular electric generator can be increased when the rotation of the engine is transmitted at a variable speed ratio to the vehicular electric generator, using the techniques disclosed in the above publications.
According to the disclosed techniques, the vehicular electric generator is operated to bring the power generating efficiency closely to an optimum operating point to seek for increased power generating efficiency and reduced fuel consumption. However, vehicles carry an electric power storage device that operates based on an electrochemical reaction, i.e., a battery, for temporarily storing electric power generated by a vehicular electric generator and supplying the stored electric power to various electric loads on the vehicle. The way in which the vehicular electric generator is required to supply electric power cannot ignore the charged state of the battery.
For example, when the vehicle is under heavy electric load conditions and the battery is discharging its stored electric energy, it is necessary to increase the electric power generated by the vehicular electric generator and shift the operating point of the vehicular electric generator for charging the battery. According to the conventional techniques, however, since the vehicular electric generator is controlled to bring the power generating efficiency closely to an optimum operating point, the vehicular electric generator may not necessarily produce enough electric power to charge the battery. If the vehicular electric generator is to generate enough electric power when the power generating efficiency is close to an optimum operating point, then the vehicular electric generator itself needs to be larger in size against the recent demands for smaller-size devices and units on vehicles.